1. Field of the Invention
This invention relates to therapeutic compositions for the treatment of acne and in particular to those compositions which contain benzoyl peroxide.
2. Prior Art
Acne and seborrhea are conditions of the human skin characterized by an excessive flow of sebum, or skin oil, from the sebaceous glands which are located in the pilosebaceous apparatus. The channel through which sebum reaches the skin surface is the duct of the hair follicle. The presence of excessive amounts of sebum in the duct and on the skin acts to block or stagnate the continuous flow of sebum from the follicular duct, thus producing a thickening of the sebum which becomes a solid plug known as a comedone. When this occurs, hyperkeratinization of the follicular opening is stimulated, thus completely closing the duct. The usual result is a papule, a pustule, or a cyst, often contaminated with bacteria which cause secondary infections. These occurences characterize the disease state known as acne, and in lesser severity, seborrhea.
Many topical therapeutic agents are employed in the treatment of acne and seborrhea to prevent the blocking of the follicular duct, to reopen the duct once it has become blocked, to act against the infecting bacteria or the thickened sebum, or to provide combinations of each of these actions. The horny outer layer of the skin is formed of dead cells composed largely of a substance known as keratin, and therapeutic agents which act to prevent the blocking of the follicular duct by promoting the removal or scuffing off of excess keratin are known as keratolytic agents. For example, the use of sulfur as a mild cutaneous irritant to remove the horny layer of skin, and with it the debris clogging the follicular openings, is well known in the art.
Benzoyl peroxide (C.sub.6 H.sub.5 CO).sub.2 O.sub.2, is a colorless, odorless, tasteless, crystalline solid that is stable at ordinary room temperatures but which is flammable and is capable of exploding when confined and subjected to grinding, heat or flame. It is a powerful oxidizing agent completely non-toxic to man, and because of its lack of local injurious effects and its lack of penetration into tissue with consequent protein precipitation, it has heretofore been proposed that benzoyl peroxide be employed as an antibacterial and keratolytic agent in the treatment of acne, and extensive clinical evaluation of this substance has conclusively demonstrated its effectiveness for this purpose.
Finely divided benzoyl peroxide is advantageously incorporated in a cream or ointment for convenience in applying it to the skin. However, because of the powerful oxidizing properties of benzoyl peroxide, the inclusion of this substance in conventional ointment or cream bases results in unstable compositions that soon display an unacceptable loss in keratolytic potency. A stable benzoyl peroxide composition that is very effective in the treatment of acne and that has a projected shelf life of over eight years is described in U.S. Pat. No. 3,535,422 to Cox and Cuifo. The Cox and Cuifo composition comprises a uniform dispersion of finely divided benzoyl peroxide particles in an emulsion of water and certain selected organic emollients. An oil and water emulsion is, by definition, a system having at least two liquid phases, and it usually comprises an oil-in-water system in which a continuous aqueous phase has dispersed therein minute droplets of a discontinuous lipid phase. When the composition is applied to the patient's skin the water content of the emulsion evaporates leaving most of the organic emollients and the benzoyl peroxide particles on the surface of the skin near and in contact with the acne sites.
After an intensive investigation of the problems involved in formulating effective and stable benzoyl peroxide-containing compositions for the treatment of acne, I have discovered and developed a composition containing benzoyl peroxide that is significantly more effective in the treatment of acne than any benzoyl peroxide-containing composition previously known in the art. My new composition employs an aqueous alcohol vehicle having a single phase that is non-lipid and that contains a non-ionic surface active agent that is soluble in the aqueous alcohol vehicle. The effectiveness of the composition appears to be due to the extremely fine particle size of the benzoyl peroxide employed, to the presence of the non-ionic surface active agent which removes skin oil from the acne sites and thereby allows the benzoyl peroxide to intimately contact and penetrate the sites, and to the absence of lipids which might otherwise inhibit the antiseptic and keratolytic activity of the benzoyl peroxide.